Integrated circuits (chips) are generally made of silicon on which electronic circuits are fabricated. These chips are placed on substrates. A substrate is made of organic materials embedded with copper interconnects. The substrate helps to join the chip to external circuits on a motherboard. FIG. 1a shows a cross-section of a chip 110 on a substrate 120. These are the two key components of an electronic module.
FIG. 2 shows a cross-section of the substrate 120. The density of connection points (controlled collapse chip connect, or C4s) 130 between the chip 110 and the substrate 120 is a critical parameter. An increased number of C4s 130 requires multiple buildup layers 150 to facilitate electrical connections to the external motherboard. Buildup layers 150 are fabricated in stages on the top and bottom of a fiber reinforced core 155.
FIG. 2 shows stacked vias 140 as well as staggered vias 145 needed to complete the interconnection. Stacked vias 140 help achieve more than 20% connection density compared to a staggered via 145. FIG. 3 shows a conventional stacked via 140 and a platted through hole (PTH) 160. A PTH 160 allows electrical connectivity between the top and bottom buildup layers.
The coefficient of thermal expansion (CTE) of various materials used to construct a module is not matched and is known to drive thermomechanical stresses within a module. Repeated thermal cycling of an electronic module exhibits failure at via interface regions due to thermomechanically driven accumulated strain.
There is a need for a system to reduce thermomechanical stresses on electronic modules.